This invention relates to an X-ray topographic system for use in examining crystal structures, for example silicon single-crystal wafers or boules for use in the production of semiconductors.
It is known to examine, for example, silicon wafers by means of X-rays to detect flaws such as slip bands which are nucleated during the rapid thermal annealing process. Such examination has hitherto been carried out by means of a Lang camera making an exposure on film. Prior art processes have suffered from a number of disadvantages, including the large size of the camera system, limitations on the size of the wafer which can be examined, and long processing times (typically about one hour for an 8xe2x80x3 or 200 mm wafer).
One object of the present invention is to provide an X-ray topographic system which is capable of examining large samples, typically up to 300 mm diameter, and carrying out examinations rapidly, typically 5 to 15 minutes.
Accordingly, the present invention provides an X-ray topographic system comprising:
an X-ray generator for producing a beam of X-rays directed towards a sample location; and
a detector positioned to receive X-rays deflected by a sample at the sample location, the detector comprising an electronic X-ray detector having an array of pixels corresponding to the beam area.
The X-ray beam may have a relatively large divergence of up to 20 milliradians.
In one form of the invention, an X-ray optic is interposed between the X-ray generator and the sample location, and is arranged to receive said beam and to transmit the X-rays as a substantially parallel beam.
In an alternative and higher resolution form, no X-ray optic is used, and any unacceptable doubling of the image is removed or compensated by software.
The detector may be positioned to receive deflected X-rays transmitted through the sample. Alternatively, the detector may be positioned to receive deflected X-rays reflected from the sample.
The X-ray generator is preferably adapted to produce a source spot size of 100 xcexcm or less and preferably has an exit window less than 20 mm from the target.
Preferably, the system resolution is about 25 xcexcm or better and the detector is located 5-10 mm from the sample location.
The X-ray optic is preferably a lobster eye optic comprising a number of X-ray reflective plates set at a slight angle from each other so that the output beam is substantially parallel. Typically, the plates are about 150 xcexcm thick and are coated with gold.
The detector is suitably a charge coupled device, most preferably a digital CCD.
The present invention also provides an X-ray topographic apparatus comprising an X-ray topographic system as defined above, stepping means for producing relative stepwise motion between the system and a sample to be inspected, the step size being a function of the beam area and spectral profile, and image processing means for reading out the pixel data of the detector between successive steps.
Other features and advantages of the present invention will be apparent from the following description and from the appended claims.